White light-emitting diodes (LEDs) are regarded as the next-generation light source because of their high efficiency, long lifetimes, weak environmental impact, absence of mercury, short response times, applicability in final products of various sizes, and many more favorable properties. White LEDs, which are gaining attention as backlight sources for liquid crystal displays of tools such as lighting, computer notebooks, and cell phones, are prepared by adding a yellow light (560 nm) emitting YAG:Ce phosphor to a blue LED. Because white LEDs prepared from blue LEDs are excited by light having a wavelength ranging from 450 to 470 nm, only a limited number of phosphors can be used. That is, only YAG:Ce-based white LEDs can be obtained using blue LEDs having a wavelength range of from 450 to 470 nm. Therefore, there is an urgent need for the development of phosphors other than YAG:Ce.
As UV LEDs are developed as an excitation light source, a new era has opened in making white LEDs with single chips. That is, by using red, green and blue phosphors with a chip having light with a wavelength ranging from 380 to 410 nm as an energy source, it has become possible to obtain a tri-color white LED with better luminescence strength and offering superior white color. Consequently, a phosphor that can be excited in the wavelength range of from 380 to 410 nm is required. In particular, a new phosphor emitting light in the range of red is needed to obtain white light with good efficiency and a high color rendering index (CRI).
WO 2006/104860 (Sarnoff Corp.) describes silicate-silica-based polymorphous phosphors according to the formula [(BvSiO3)x(Mv2SiO3)y(Tv2(SiO3)3)z]m(SiO2)n:Eu, Mn, X, wherein X is a halogenide. A drawback of these halogenide-containing phosphors is a lack of chemical stability.
WO 2008/047965 describes a luminescent material of the formula (Ca,Sr,Ba)αSiβOγ:Eu, Mn, M, N, wherein M is at least one cation selected from the group consisting of Ce, Pr, Sm, Gd, Tb, Dy, Ho, Er, Tm and Yb and N is at least one cation selected from the group consisting of Li, Na, K, Al, Ga, In and Y.